In recent years, in the field of a transmission for a vehicle, a so-called dual clutch transmission (DCT) for continuously transmitting power from a power source to wheels as a driving force is known.
The dual clutch transmission has the following configuration. That is, the dual clutch transmission includes a first transmission mechanism including odd-numbered gear shift stages, a second transmission mechanism including even-numbered gear shift stages, a first clutch interposed between a power source and the first transmission mechanism, for transmitting power from the power source to the first transmission mechanism or shutting off the transmission of the power, and a second clutch interposed between the power source and the second transmission mechanism, for transmitting power from the power source to the second transmission mechanism or shutting off the transmission of the power.
Moreover, in recent years, there exists even a hybrid vehicle having the above-mentioned dual clutch transmission installed thereon. As one hybrid vehicle described above, a hybrid vehicle having the following configuration is known. That is, a mechanical power source such as an engine is used as the power source arranged via the first clutch and the second clutch, and an electrical power source such as a drive motor is arranged as another power source on an input shaft of any one of the first transmission mechanism and the second transmission mechanism.
However, the above-mentioned hybrid vehicle has the following problem. That is, during the deceleration in the hybrid vehicle, in some cases, any one of the first clutch and the second clutch is disengaged, and the mechanical power source is stopped, to thereby perform regenerative control of the electrical power source.
On this occasion, in the hybrid vehicle, for example, a gear shift request of shifting between the respective gear shift stages of the transmission mechanism to which the electrical power source is coupled may be made during the regenerative control through the deceleration. On this occasion, when the gear shift request is made during the regenerative control through the deceleration, all synchronizer mechanisms in the transmission mechanism on the drive motor side are brought into a free rotation state. As a result, a state in which a motor torque becomes zero, namely a so-called torque drop, is caused, and a driver feels a sense of discomfort.
As a method of solving this problem, there is proposed a method of suppressing the torque drop by adjusting the torque of the second clutch in a range less than a cranking torque so as to maintain a braking force upon the gear shift during the regenerative travel (for example, refer to Patent Literature 1).
Moreover, there is proposed a method of suppressing the torque drop by engaging the first clutch once during the regeneration travel to generate an engine brake, and adjusting the torque of the second clutch upon the gear shift (for example, refer to Patent Literature 2).
Further, there is proposed a method of suppressing the torque drop by using a brake cooperation system capable of adjusting brakes on wheels independently of a depression amount of a brake pedal, and adjusting friction brake amounts on the wheels in an area where a torque of the drive motor needs to be 0 for the gear shift (for example, refer to Patent Literature 3).